Generating Fock-state superpositions from coherent states by selective measurement

TL;DR

This paper presents a simple, measurement-based protocol to generate specific Fock states and superpositions from a coherent state in a resonator, achieving high fidelity with minimal measurements and extending to entangled states.

Contribution

A novel measurement-driven protocol for generating arbitrary Fock states and superpositions from coherent states without tailored driving, applicable to multi-resonator systems.

Findings

Achieves over 99% fidelity for Fock states with n~10 in less than 30 measurements.

Extends to generate Bell-like entangled states between resonators.

Analyzes fidelity and success probability considering decoherence effects.

Abstract

Fock states and their superpositions are exotic testbeds for nonclassical physics and valuable resources for quantum technologies. We provide a simple protocol for the quantum measurement to generate an arbitrary Fock state and certain superposed Fock states from a coherent state of a target resonator, without any carefully tailored driving. This conditional protocol can be efficiently constructed by a sequence of joint free evolution of the resonator and an ancillary qubit, which are coupled via a Jaynes-Cummings interaction, and projective measurements on the qubit. By properly choosing the duration of each evolution-measurement cycle and the initial state of the resonator, we can generate a desired Fock state $|n\rangle$ and a superposed Fock state $(|0\rangle+|n\rangle)/\sqrt{2}$, $n\sim10$, with a fidelity over $99\%$ in less than $30$ measurements. Moreover, our protocol can be extended straightforwardly to the generation of a Bell-like state $(|00\rangle+|nn\rangle)/\sqrt{2}$ with multiple excitations in a double-resonator system. We also calculate the outcome fidelity and the success probability of our protocol in the presence of decoherence.